The present invention relates to a width-extensional mode quartz crystal resonator having specific features of a KT cut angle, thickness-to-width ratio, configuration and excitation electrode structure. Particularly, the invention relates to the width-extensional mode quartz crystal of the type most suitable for use in a reference signal source of pagers, IC cards, and vehicle telecommunication, in which is required a resonator having a compact size, high accuracy, shock resistance and low cost.
Conventionally, a thickness shear mode quartz crystal resonator is used in a frequency range over 4 MHz. The oscillating frequency of this type of resonator is determined substantially by its thickness. Particularly, there is preferably used an AT cut type of the resonator which features a good frequency temperature behavior. This type of the resonator is produced by mechanical machining. However, the conventional AT cut quartz crystal resonator is difficult to mount when its size is reduced since it is formed by mechanical working, thereby causing an increase in a series resistance R.sub.1 and causing generation of a spurious response. Thus, miniaturization of the resonator is limited. Further, this type of the resonator has various drawbacks such as poor shock resistance and limitation in cost reduction because of the individual machining of the resonator element, when used as a very small size oscillating source in various portable instruments. Thus, there has been long desired a quartz crystal resonator having a new cut angle and new shape which features an oscillating frequency over 4 MHz, very small size, reduced series resistance R.sub.1, zero temperature coefficient and applicability of being formed by an etching process.